1. Field of the Invention
This invention relates generally to drilling oil and gas wells and particularly to methods and apparatus for flushing wells.
2. Brief Description of the Background Art
In the drilling and production of oil and gas wells, adverse conditions may arise which cause the drill string to become stuck. For example, the formation of key seats in the wall of the well bore, the caving in of the formation or the settling of drilling mud or cuttings may require time consuming wash over or fishing operations before the well can be completed.
Many drill strings include a jarring mechanism to aid in the prevention of drill string sticking and the release of the drill string upon the occurrence of sticking. By the employment of a mechanism of this kind, it is often possible to quickly release the string in the event of sticking or to loosen a broken or disconnected portion of a drill pipe or other object which has become stuck in the well.
It is also well known to use a flush valve to selectively flush the return annulus of the drill hole to help free the string during jarring. Flushing may be used during a fishing job to retrieve junk from the hole. A surge of water rushing towards the drill bit helps to free a stuck drill string or to clear junk for grappling and removal.
The operation of conventional drilling flush valves may disrupt the normal operation of the drilling string. In conventional flush valves the bore of the drill string is interrupted or "clogged" to operate the valve. For example, in one conventional flush valve, a ball is dropped into the string to shear a pin to open the flush valve. As a result the bore cannot thereafter be fully utilized as channel for communication with the region of the string at or below the valve area. After a flush valve is operated it may be desirable to run a "free point" indicator through the bore to determine where, if anywhere, the string is stuck. In addition, it may be desirable to run various tools or instruments by wireline or otherwise through the bore, past the flush valve. Moreover, in conventional flush valves it may not be possible to close the valve after it has been opened, without removing the string from the hole. Thus, for these reasons, it must be appreciated that the operation of such valves may severely interrupt the normal operation of the string.